1. Technical Field
The present disclosure relates generally to orthopedic spinal surgery, and more particularly, to devices, systems, and methods for guiding a cervical drill, bone screw or other instrument during spinal surgery.
2. Background of Related Art
The spinal column is a complex system of bones and connective tissues that provide support for the human body and protection for the spinal cord and nerves. The adult spine is comprised of twenty-four vertebral bodies, which are subdivided into three areas, including seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. Between each vertebral body is an intervertebral disc that cushions and dampens the various translational and rotational forces exerted upon the spinal column.
There are various disorders, diseases and types of injury which the spinal column may experience in a lifetime. These problems may include, but are not limited to, scoliosis, kyphosis, excessive lordosis, spondylolisthesis, slipped or ruptured discs, degenerative disc disease, vertebral body fracture, and tumors. Persons suffering from any of the above conditions typically experience extreme or debilitating pain and often times diminished nerve function.
One of the more common solutions to any of the above mentioned conditions involves a surgical procedure known as a spinal fusion. Spinal fusion involves fusing two or more vertebral bodies together to eliminate motion at the intervertebral disc or joint. To achieve spinal fusion, natural or artificial bone, along with a spacing device, replace part or all of the intervertebral disc to form a rigid column of bone. Mechanical hardware is connected to the adjacent vertebrae to stabilize the spine in that area while the bone grows and the fusion occurs.
The mechanical hardware used to immobilize the spinal column typically involves a series of bone screws and metal rods or plates. When the spine surgery is performed posteriorly, it is common practice to place pedicle bone screws into the vertebral bodies and then connect a metal rod between the screws, thus creating a rigid structure between adjacent vertebral bodies. When the spinal surgery is performed anteriorly, it is common practice to attach a thin metal plate directly to the vertebral bodies and secure it to each vertebral level using one or more bone screws. For the remainder of this disclosure, references to spinal surgery will be referring to the anteriorly performed surgery in which a metal plate is secured directly to the vertebrae using bone screws.
Because the spine is routinely subject to mechanical loads which cycle during movement, a primary concern of physicians performing metal plate implantation surgeries, as well as of the patients in whom the implants are placed, is the risk of screw pullout. This is of particular concern in the cervical region because of the critical vessels that abut the anterior surfaces of the cervical spine. Screw pullout occurs when the cylindrical portion of the bone that surrounds the inserted screw fails. A bone screw that is implanted into the vertebrae perpendicular to the plate is particularly weak because the region of the bone that must fail for pullout to occur is only as large as the outer diameter of the screw threads. Screws which are angled inward towards one another, also referred to as “toe-nailed”, or ones which diverge within the bone have been found to greatly reduce the likelihood of screw pull out because the region of bone that must fail is increased as compared to that of screws implanted perpendicular to the plate.
The metal plates used to connect the vertebrae in spinal surgery are well known in the art. These plates may define any number of openings configured for receiving bone screws. The openings for receiving the screws may include a beveled or angled edge for more securely receiving the angled screws. The metal plates may also include openings or grooves for releasably receiving an elongated handle member for maintaining the metal plate during implantation. Because the metal plates used in spinal fusion are relatively small and awkward to handle, elongated handle members have been developed for releasably engaging the metal plates such that they may be held in position while the bone screws are being applied. The elongated handle members generally include a handle assembly for grasping the handle member and an extension member connected thereto. The distal end of the extension member may include any number of clips, protrusions, tabs or the like for releasably engaging the metal plate.
As discussed above, positioning of the bone screws used to secure the metal plate to the vertebrae is important to preventing screw pullout, and thus a successful spinal fusion. The elongated handle members may further be configured to include a guide member for guiding the drill, screws or other instrument for assisting a surgeon in positioning the bone screws during implantation of the metal plate. Commonly owned U.S. Pat. No. 7,094,242 to Ralph et al., discloses such a device, and is incorporated herein by reference in its entirety.
Conventional drill guides generally include a handle assembly fixedly attached to the proximal end of an extension member. The distal end of the extension member generally includes a mounting assembly configured for releasable engagement with a metal plate. The extension member may be configured to include one or more guide members. Alternative drill guides include a guide member that is independently attached to the mounting assembly. During procedures involving surgeons with different preferences, more than one surgeon or the use of multiple instruments within the surgical field, the handle assembly of the drill guide often is oriented in a less than convenient position. Because the handle assembly is fixedly attached to the extension member, the orientation of the handle assembly cannot be adjusted. Furthermore, because the handle is fixedly attached to the extension member it cannot be removed, and thus, cannot be replaced. In the event that the handle assembly becomes worn or damaged, the only option is to replace the entire drill guide.
Therefore, it would be beneficial to have a drill guide apparatus including a handle assembly that can be selectively positioned about an extension member prior to or during implantation of a metal plate. It would further be beneficial to have a handle assembly that can be removed from the extension member.